LPG is not so good in an engine designed to run on 'solid fuel' [Petrol/gasoline] but in an engine that has been designed specifically for the dry, gaseous fuels [LPG] it can equal or better the solid fuel engine. [Yes I know petrol/gasoline is a liquid, but apparently it's a proper trade term]

The secret to success with LPG is compression & something like 10.5 to 1 or 11 to 1 is a good starting point apparently.

If this works out like it's supposed to, then the dedicated LPG engine will be the equal of the petrol/gasoline engine in terms of actual consumption & streets ahead in terms of co$t to run.

This can actually be measured on a dyno that is set up to measure BSFC [Brake Specific Fuel Consumption] This measures the fuel used per hour, in pounds weight per horsepower. [Kg per Kw per hour] & is usually run at different power settings as the weight of fuel consumed per horsepower per hour will vary at different power settings & engine speeds.

It can be a real eye opener & is a measure of the efficiency of a particular design & state of tune.

Thanks to you guys, this thread is really interesting indeed. Informative too.

David I forgot about the Nifty Fifty ad and the "plus" model. I found an article online where an owner of one said he got upper 40 mpg's in the mountains with one, and as much as 56 mpg on a highway trip when he was really driving for best mileage!

You're right. I should be aiming at 60 or 65 mpg!

This will be a fun project, but to be honest things like fuel injection or lpg conversions are out of the question for me. I will focus on maximizing the standard equipment pretty much. I will use my '76 A14 short block, with a set of A15 [basically flat top] pistons for best compression. I'll stay with the standard cam and use the '80 A14 small round port 990 head on it. I do have a wide band oxygen sensor setup on the car and will be able to jet the carb for max efficiency. The car does have a Pacesetter header on it and a mandrel bent 2" exhaust system with a low restriction muffler. They will stay of course, but as noted really aren't needed for the low engine speeds I will be using.

The A15 piston used a lower deck height than the A14 because, with the same rod as the A14, the A15 crank pushed the wrist pin higher up the bore, so a lower crown was needed to prevent the piston from poping out the top.
In an A14 it will fall short of the top of the block by about 2.5mm.
Addidionally, because the piston in an A15 displaced an additional 22cc of air in it's journey from the bottom to the top, & it was trying to squeeze it into the same size combustion chamber as the a14, it became necessary to make a deeper bowl in the piston crown to bring the compression ratio to about the same as the previous engines.

With A15 pistons you will drop the compression by a significant amount & even the squish band will be non functioning with the piston falling short by 2.5mm so this can't be good.
Even flat top A15 pistons wont save it.

The beauty of the later intake manifolds is the fact that they are water heated so make sure that this feature is fully operational even if you enlarge the holes under the ports fractionally with a drill.

You know, drivers of more powerfull cars may pass you easily on the freeway, but the smile you get when you top up the tank for pocket change while they re-mortgage the house to fill up can make it worthwhile sometimes. I know it does for me, particularly when fuel prices hit a record high recently. I was laughing all the way to the bank.

P.S. What most people never realise is that the most efficient engine is a constant speed engine as all of the parameters can be tailored to this specific operating environment for maximum benefit.
This is why large reciprocating piston aircraft engines are constant speed engines using the prop pitch like a sliding ratio trans to handle speed & load.

This is why professional 'economy drivers' try to keep their vehicle speed, & at least the engine speed, within a narrow rpm band wherever possible. Once this optimum engine speed is determined, keeping it there is an edge you can use.

Thanks for the correction on the A15 pistons Dodgeman. I remember using a set to increase compression on my E16. They are a direct replacement for the E-series. I have a thread about it with pics here. You're right, they won't work properly in an A14.

Yes I like the water heated feature of the late intakes. The round port intake I gave away had them! It's getting harder these days to find these old parts, but I'll get another intake one way or the other. If anyone's got one please let me know.

My pleasure, were here to hopefully help each other.

EDIT
I had a look at your link & clearly, your a15 pistons are VERY different from ours, so US model A15's must have a larger combustion chamber that the Aussie spec ones in order to have the same or similar compression ratio's. We NEED US spec A15 pistons.

Your US spec A15 piston.






























My Aussie spec A15 pistons.
Left side is a factory A15 piston with a new 'replacement' A15 piston on the right.
These have noticeably more bowl than US ones.
The rods are from an A12T [120Y GX] [left] & A12A [right]

blownb310
If it comes down to it I can check availability through Nissan. Just need the application info. I'm guessing 77 GFU model maybe?
All I have is A12 stuff and am not sure if I have an intake.

Kelmo

Thanks Kelmo,

The head I've got is the 990 casting from an '80 210 SL hatchback with an A14. I would imagine any round port water heated intake will work though.

Mike

I've found a round port Datsun 310 [N10] FWD intake manifold, but it does not have the correct angle for the carburetor that the RWD manifold has. Does anyone think that will be a problem?

Also, besides the Nismo competition head gasket [11044-M0822] are there any other [less expensive] A-series head gaskets that have the larger 79mm bore size I need for my 1608?

Thanks,

Mike

whats the difference with the fwd manifold? does it sit lower like the vanette manifolds?

Quote:I haven't purchased it yet, but here's a picture of it.




I am assuming that a FWD manifold won't have the angle built into it that keeps the carburetor level when installed on the RWD engine that leans back in the chassis.